1. Field of the Invention
This invention relates to devices for cleaning the exhaust gases exhausted particularly from internal combustion engines, and more specifically to improvements in the secondary air supply means of the exhaust gas cleaning devices of the type in which the exhaust gases are burned or catalytically reacted in a reaction chamber, provided intermediate of the exhaust pipe, with secondary air introduced thereinto, whereby the toxic unburned components in said exhaust gases are oxidized and rendered innoxious.
2. Description of the Prior Art
Conventional exhaust gas cleaning devices of the type described comprise a reaction chamber, i.e., a direct flame type or catalytic combustion chamber or catalyst means, provided intermediate of the exhaust pipe connected with the exhaust manifold, and means for supplying secondary air from an air pump into the exhaust pipe upstream of said reaction chamber. In such exhaust gas cleaning devices, it has been proposed to construct the upstream side of the exhaust pipe with respect to the reaction chamber into a double wall structure and supply the secondary air to be mixed with the exhaust gases through the outer chamber surrounding the inner wall of the exhaust pipe so that said secondary air may be heated by the heat of the exhaust gases. Such an arrangement of the secondary air supply means is effective for maintaining the temperature of the exhaust gases and thereby promoting the combustion or catalytic action with the reaction chamber because, since the heat of the exhaust gases is absorbed by the secondary air once and then returned to said exhaust gases, substantially no heat is released from the exhaust gases into the atmosphere. However, on some occasions, an undesirably intense combustion or catalytic reaction takes place within the reaction chamber depending upon the operating condition of the internal combustion engine, resulting in overheating of the catalyst or the structural members of the reaction chamber and thermal failure of the same. Under such an operating condition of the engine, the temperature of the exhaust gases also becomes high and accordingly the temperature of the exhaust pipe becomes excessively high. In order to deal with such problems, it has been proposed to provide a bypass valve on the exhaust pipe at a location upstream of the reaction chamber and bypass the exhaust gases so as to pass them through the reaction chamber. However, such an arrangement is defective in that the exhaust pipe diverges into two lines and becomes complicated in construction.